Lemma 3.11 ([1]}) 
For every \(\varepsilon >0\)  there is a constant \(C_\varepsilon >0\)  such that for each \(k\in \mathbb {N}\)  we have
\(\int _0^1\big |f_{X}(\xi )\big |^{k(k+1)}{\rm d}\xi \le C_\varepsilon N^{k^2+\varepsilon }.\) 

